The present invention relates to light-emitting devices and particularly to those devices intended to produce a beam in a selected direction such as toward a target of interest. The invention provides motion-compensation technology suitable for use with such light-emitting devices, which may dampen and/or substantially eliminate the effect of unintentional motion, vibration, or movements, such as angular movements, caused by mechanical vibrations, hand tremors, and so forth.
Light-emitting devices, such as laser diode devices, are used in a variety of consumer, computer, business, medical, scientific, military, outdoor, telecommunication and industrial products, including but not limited to compact disk (CD) players and computer CD-ROM drives, digital video disk (DVD) players and DVD-ROM drives, laser printers, laser pointers, barcode scanners, measurement devices, rangefinders, scopes, industrial material processing devices, marking and cutting systems, medical equipment, fiber optic transmission systems, satellite communications, and digital printing presses. Many of these applications require precision accuracy for successful implementation. However, conventional light-emitting devices may be affected by unintentional angular movements (e.g., fine vibrations from the machine in which a laser is encased, fine tremors from a shaking hand holding a laser, etc.) and, as a result, generate an unsteady column of light—producing an effect that may cause inferior performance.
An example of the above mentioned effect will now be described with reference to a laser pointer. Fine tremors of the human hand, when holding even a lightweight laser pointer (or other pointing device), have been measured at a frequency range of 1 to 5 Hz. These unwanted vibrations are often amplified when the person maneuvering the device is nervous. The resulting deviation of the projected spot from the intended target point to the actual point is proportional to the distance from the pointing device to the target object (e.g., a point on a screen). This deviation may be approximately equal to the product of the sine or the tangent of the angle and the distance to the projected spot. In other words, for small angular movements (such as less than 10 degrees), the movement of the projected spot is approximately equal to the product of the distance to the target and the angle of the movement (in radians). For instance, small angular movements of +/−1 degree of a laser pointing device may result in movements of approximately +/−2 cm of the projected spot on a target 1 meter away; and, these angular movements will result in a 10-fold larger projected spot movement (approximately +/−20 cm) for a target 10 meters away (which may be typical of large lecture halls). In contrast to angular movements, translational movements (sideways movements of the hand) are not amplified by the distance from the light-emitting device to the target object. That is, if the hand holding a laser pointer is moved sideways by 1 cm, the spot on the target is also moved sideways by 1 cm irrespective of how far the target is from the hand. Thus, only the angular changes (particularly those in the 1 to 5 Hz frequency region, typical for a hand tremor) cause the undesirable movements of the projected light on the target.